At the dyeing treatment of hair, it is most common to use a double preparation type oxidative hair dye comprising a first preparation containing a hair swelling agent such as ammonia and an oxidative dye intermediate and, if necessary, a coupler, and a second preparation containing an oxidizing agent such as hydrogen peroxide. The mechanism of hair dyeing in the double preparation type oxidative hair dye includes swelling of hair by the first preparation to permeate the oxidative dye intermediate, the coupler, and the like into the hair and subsequent oxidative polymerization of the oxidative dye intermediate and the like in the hair by the second preparation to develop a color, thereby hair dyeing being completed. The hair dyeing by this method is excellent in hair-dyeing ability and also can create a variety of color tones by blending various couplers for hair dyeing in combination with an oxidative dye intermediate and the like, so that the method is widely utilized.
Recently, in order to alleviate the damage of hair, a technology of using an oxidase instead of hydrogen peroxide to be used in the second preparation has been reported (see, e.g., Patent Document 1). Since the oxidase is used, single preparation type one wherein the second preparation is combined with the first preparation in the absence of oxygen becomes possible. Also, there has been utilized a single preparation type oxidative hair dye wherein an oxidative dye intermediate and the like undergo oxidative polymerization through uptake of oxygen in the air as an oxidizing agent after the application to hair.
However, a dye component in a hair dye base is high in reactivity, and therefore, there has been an inconvenience that, even at a stage in which the hair dye is stored before it is applied to hair, a polymerization occurs in the presence of oxygen in the air and thereby color is developed. Accordingly, various types of improvements for solving the above inconvenience have so far been made.
As one method, there may be mentioned a method of blocking the air from the hair dye. Namely, an improvement has been made such that the hair dye is produced or allowed to be a commercial product in an atmosphere in which the hair dye is hardly in contact with oxygen by removing oxygen dissolved in a base or by purging a container to which the base is stored with an inert gas which does not cause a reaction or the like. For example, there has been known a technology of conducting a mixing operation of components constituting a hair dye composition under an atmosphere having an oxygen concentration of 0.00015% or less (Patent Document 2). However, in order to perform such an operation, there still remains an inconvenience that suitable apparatus/equipments are required and hence economic burden for them is large. Furthermore, since highly reactive dye compounds are still apt to be degenerated and the hair dyeing effect comes to be deteriorated with time, it is necessary to pay a considerable effort for maintaining the value as a commercial product.
In that respect, a method of using a chemical agent is economically advantageous and there is known a technology for preventing degeneration or the like of a highly reactive dye compound and inhibiting the deterioration of the hair dyeing effect over time by adding a reducing agent such as a bisulfate salt or vitamin C (ascorbic acid and a salt thereof) into the base to trap active species to be generated in the base.
Moreover, there has been known a technology of adding mercaptans such as thioglycolic acid, thiolactic acid, or mercaptosuccinic acid into a base to stabilize a dye compound (see, e.g., Patent Document 3, Patent Document 4, etc.). Although the method is effective to some extent, it still has not only a defect that the mercaptans used gives out a very strong offensive smell and thus makes an operator or the like unpleasant but also an inconvenience that the amount of the chemical agent to be used is large and thus it damages the hair and irritates the skin. Furthermore, in the case where mercaptans is applied to an actual commercial product, there sometimes arises a problem that it exerts an influence on the blending balance of an oxidative dye intermediate and a coupler, or the like.
In addition, a technology of incorporating an iron ion into mercaptans has been reported (Patent Document 5), but the above inconvenience is still not solved even in the technology. Moreover, a technology of utilizing a mercapto compound such as thioglycerol, thiolactic acid, thiomalic acid, or cysteamine as a polymerization inhibitor for oxidative dyes has been reported (Patent Document 6). However, these compounds are only listed in the specification but no specific effects are confirmed in Examples or the like.
Patent Document 1: JP-A-6-172145
Patent Document 2: JP-A-2000-344638
Patent Document 3: JP-A-55-6570
Patent Document 4: JP-A-4-312515
Patent Document 5: JP-A-9-315948
Patent Document 6: JP-A-2005-162681